I have been testing some RS485 communications of recent, and found the need for some flexible adapters for the above interface box. The adapters are to provide selectable line termination and fail-safe bias. Continue reading RS485 termination / bias adapter

AIM also claims to have a means of backing out a known transmission line between reference plane and DUT. This article discusses use of AIM’s Refer to Antenna facility.

AIM’s developer recently said of AIM’s Refer to Antenna facility:

Version 882 does have a problem with the Refer to Antenna function. Version 865A can be used for this function.

This function does have it’s limits though. It should only be used for good quality coax. The impedance and velocity factor of coax is not constant over the whole length and this limits the accuracy. Also the impedance may not be equal to the “nominal” impedance in the catalog. The impedance of 50 ohm cable can vary quite a bit. AC6LA.com has some interesting data showing how coax parameters vary with frequency.

Custom cal is much better when it is possible to put the cal loads at the far end of the transmission line. This takes into account variations in impedance, velocity factor, and loss and it can be used when there is coax and ladder line in one transmission line system.

This article demonstrates a simple method of measuring the complex common mode impedance of a Guanella 1:1 current balun using a one port VNA, though of course the technique is equally applicable to a two port VNA.

This article shows a simple method of measuring the complex common mode impedance of a Guanella 1:1 current balun using a modern Antenna Analyser.